Photosynthesis & Leaf Structure (Cambridge (CIE) IGCSE Biology)

Fig. 1 is a photomicrograph of a cross-section of part of a leaf.

Fig. 1

(i)

Draw a large diagram to show the layers present in the leaf section shown in Fig.1.

Do not draw any cells.

[3]

(ii)

Measure the thickness of the leaf along the line AB on Fig.1.

Calculate the actual thickness of the leaf using your measurement and the formula.

Include the units.

[3]

(iii)

Fig. 2 shows a photomicrograph of cells from one type of tissue found in leaves.

Fig. 2

Label the layer on your drawing, with the letter X, to show where this type of tissue is found.

[1]

Scientists carried out an investigation into the effect of light on the growth of leaves.

Plants of the same species (A) were grown in three different light intensities.

The plants were grown in the same soil and kept in glasshouses with automatic watering.

A sample of 100 leaves was selected at random and collected from plants in each of the three different light intensities. A total of 300 leaves were collected.

The scientists studied the variations in the size and structure of the leaves in each sample.

(i)

Suggest why the scientists used large samples of leaves.

[1]

(ii)

Suggest why the leaves in each light intensity were selected at random.

[1]

(iii)

A grid, divided into millimetre squares, was used to measure the surface area of the leaves.

Outline how the grid could have been used.

[2]

(iv)

State the variable that was changed (independent variable) in this investigation.

[1]

The scientists collected data from one other plant species (B).

Table 1 shows the results.

Table 1

(i)

Calculate the percentage difference in the average leaf area for species A from a light intensity of 50 arbitrary units to 10 arbitrary units.

Show your working and give your answer as a percentage to the nearest whole number.

[2]

(ii)

Plot a bar chart on the grid to show the average leaf area for species A and B, at each light intensity.

[4]

(iii)

Describe the trends shown in your graph for species A and species B.

[2]

(iv)

The scientists want to determine more precisely the light intensity that results in the largest leaf area for species B.

Suggest how the method used in the investigation could be modified to achieve this.

[1]